Challenges or Points to be considered while migrating: SRM on ECC to SRM on S4HANA

We have a scenario where one of our Client is already having ECC and SRM (P2P & Sourcing) setup in their procurement landscape.

Now client has decided to move from ECC backend to S4 HANA. And with SRM already live & running, they want to use the same SRM Business Suite when migrated to S4 HANA (instead of using inbuilt HANA - Self Service Procurement).

Please help me with some light on challenges/major points to be considered from SRM standpoint, when backend is moved from ECC to S4 HANA.